Looking for piece of mind...?

i'm just looking for piece of mind more than anything else. I had unprotected on the 18th of december and I was due my period on the 13th of this month, they haven't come. I've taken a hpt this morning which came up negative. I'm just wondering since it's been 33 days since I had and my periods are already 6 days late if I was pregnant, it surely would have showed up positive by now..? I've been worrying a lot, this could be the cause of my late period. I used an early detection test also